1. Field of the Invention
The present invention generally relates to rotary vane pumping machines, and more particularly, to a vane slot roller assembly that provides a friction-reducing, momentum-transferring interface between the vanes and slot walls in a rotor of a rotary vane pumping machine, and an installation method for the assembly.
2. Description of the Related Art
The overall invention relates to a large class of devices comprising all rotary vane (or sliding vane) pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines. Herein the term pumping machine refers to a member of a set of devices including pumps, compressors, engines, vacuum-pumps, blowers, and internal combustion engines. Thus, this invention relates to a class of rotary vane pumping machines.
This class of rotary vane pumping machines includes designs having a rotor with slots with a radial component of alignment with respect to the rotor's axis of rotation, vanes which reciprocate within these slots, and a chamber contour within which the vane tips trace their path as they rotate and reciprocate within their rotor slots.
The reciprocating vanes thus extend and retract synchronously with the relative rotation of the rotor and the shape of the chamber surface in such a way as to create cascading cells of compression and/or expansion, thereby providing the essential components of a pumping machine.
Some means of radially guiding the vanes is provided to ensure near-contact, or close proximity, between the vane tips and chamber surface as the rotor and vanes rotate with respect to the chamber surface.
Several conventional radial guidance designs were described in the background section of pending U.S. patent application Ser. No. 08/887,304, to Mallen, filed Jul. 2, 1997, entitled "Rotary-Linear Vane Guidance in a Rotary Vane Pumping Machine" ('304 application). The '304 application describes an improved vane guidance means in order to overcome a common shortcoming of the conventional means of guiding the vanes, namely that high linear speeds are encountered at the radial-guidance frictional interface. These high speeds severely limit the maximum speed of operation and thus the maximum flow per given engine size.
In the improved sliding-vane pumping geometry of the '304 application, multiple vanes sweep in relative motion against the chamber surfaces, which incorporates a radial-guidance frictional interface operating at a reduced speed compared with the tangential speed of the vanes at the radial location of the interface. This linear translation ring interface permits higher loads at high rotor rotational speeds to be sustained by the bearing surfaces than with conventional designs. Accordingly, much higher flow rates are achieved within a given size pumping device or internal combustion engine, thereby improving the performance and usefulness of these machines.
However, even with the above advantages, efforts continue in order to further refine and enhance the performance of the rotary machine. In particular, rollers of a rolling frictional interface between the reciprocating vanes and the walls of the slots must be properly distributed along the wall between the vane and its slot to simultaneously reduce friction and transfer momentum between the rotor and the vanes. However, because these vane slot rollers are disposed in a slot that is part of a rotating rotor, a centripetal acceleration force may subject the rollers to severe misalignment in the radial direction. That is, the vane slot rollers have a tendency to congregate at the outward portion of the rotor slots, where the rollers do not provide adequate friction reduction and momentum transfer for the portions of the vane closer to the rotor axis, especially when the vane is retracted into the slot. In addition, the shift of rollers to the outward portion of the rotor slots is accompanied by roller slippage which causes excessive wear on the rollers themselves, shortening their useful life.
Furthermore, simple cylindrical rollers do not provide axial control for the vanes. As a result, the vanes may drift from one axial side of the rotor to another, leading to increased friction and wear with the axial sides of the chamber and variable performance during the operation of the rotary vane pumping machine.
Therefore, there is a need for vane slot rollers which are properly aligned with the vane and slot walls, which do not slip, and which provide enhanced control of the axial position of the vane.